The present invention relates to a carriage guide mechanism especially adapted for use with a scanning type information processing device of the type wherein an image reading head or an image recording head is reciprocated along a rectilinear path in parallel with a drum around which is wrapped an original or a recording medium and is spaced apart from the drum by a predetermined distance.
A prior art carriage guide mechanism of the type described above comprises in general a head carriage by a lead screw and guided by a guide bar. The lead screw and the guide bar are extended through the head carriage in parallel with the axis of the drum and are supported at their ends by supporting frames which also support the drum. Alternatively, the carriage is guided by first and second guide bars in a manner substantially similar to that described above. The carriage is displaced in either direction along the lead screw and the guide bar or along the first and second guide bars so as to scan the information bearing medium or the recording medium wrapped around the drum in the axial direction thereof. However, even a slight lack of parallelism between the two guide means and/or twists or torsions thereof result in the unsmooth movement of the carriage which in turn causes the variation on a driving system. As a result, the variation in speed of the head occurs so that the correct reading or recording cannot be accomplished. In the case of recording, the recorded images are degraded with fringe patterns.
In order to attain a high parallelism between the two guide means, they must be manufactured to the very close tolerances and assembled with the supporting frames also with the very severe tolerances. As a result, the manufacturing cost as well as the assembly cost are considerably increased.
Furthermore, since the two guide means are extended through the carriage, the latter cannot be swung away from the drum. In other words, the distance between the carriage and the drum which is very small remains unchanged over the whole length of the drum so that it is very inconvenient to make the inspection, maintenance and replacement of the head in such small space between the carriage and the drum.